I have been using an EDTA-tris pre-treatment for resistant, difficult pseudomonas cases. EDTA-tris damages the cell membranes of the gram negative bacteria so that the topical antibiotics can penetrate and kill the bacteria. Fill the ear canal(s) with the EDTA-tris solution and allow it to remain in the ear for 15 minutes. Then wipe out whatever comes out and instill the antibiotic solution.

Even though your culture may show resistance to most antibiotics, pretreatment with EDTA-tris makes this issue less important. You can probably use any of the fluroquinolones topically, even though your sensitivity didn't indicate sensitivity to them. Remember that cultures are taken reflect the blood levels of an antibiotic and that if they are given topically they will be typically 100-1000x that in the blood.